Tutorial by Examples: a

The srcdoc attribute can be used (instead of the src attribute) to specify the exact contents of the iframe as a whole HTML document. This will yield an IFrame with the text "IFrames are cool!" <iframe srcdoc="<p>IFrames are cool!</p>"></iframe> If the...

jQuery code is often wrapped in jQuery(function($) { ... }); so that it only runs after the DOM has finished loading. <script type="text/javascript"> jQuery(function($) { // this will set the div's text to "Hello". $("#myDiv").text("Hello"...

These are all equivalent, the code inside the blocks will run when the document is ready: $(function() { // code }); $().ready(function() { // code }); $(document).ready(function() { // code }); Because these are equivalent the first is the recommended form, the following is a ...

When a user subscribes to a channel, you may want to set state for that newly subscribed user. While there is a subscribe with state API, there are some scenarios where this is not the most optimal/reliable technique (like during a disconnect/reconnect situation - the state will be lost and not rein...

To remove an element inside an array, e.g. the element with the index 1. $fruit = array("bananas", "apples", "peaches"); unset($fruit[1]); This will remove the apples from the list, but notice that unset does not change the indexes of the remaining elements. So $fr...

Boolean is a type, having two values, denoted as true or false. This code sets the value of $foo as true and $bar as false: $foo = true; $bar = false; true and false are not case sensitive, so TRUE and FALSE can be used as well, even FaLsE is possible. Using lower case is most common and recom...

A cookie is set using the setcookie() function. Since cookies are part of the HTTP header, you must set any cookies before sending any output to the browser. Example: setcookie("user", "Tom", time() + 86400, "/"); // check syntax for function params Description: ...

Retrieve and Output a Cookie Named user The value of a cookie can be retrieved using the global variable $_COOKIE. example if we have a cookie named user we can retrieve it like this echo $_COOKIE['user'];

The value of a cookie can be modified by resetting the cookie setcookie("user", "John", time() + 86400, "/"); // assuming there is a "user" cookie already Cookies are part of the HTTP header, so setcookie() must be called before any output is sent to the...

Use the isset() function upon the superglobal $_COOKIE variable to check if a cookie is set. Example: // PHP <7.0 if (isset($_COOKIE['user'])) { // true, cookie is set echo 'User is ' . $_COOKIE['user']; else { // false, cookie is not set echo 'User is not logged in'; } ...

var='0123456789abcdef' # Define a zero-based offset $ printf '%s\n' "${var:3}" 3456789abcdef # Offset and length of substring $ printf '%s\n' "${var:3:4}" 3456 4.2 # Negative length counts from the end of the string $ printf '%s\n' "${var:3:-5}" 3456789a...

cat < file.txt Output is same as cat file.txt, but it reads the contents of the file from standard input instead of directly from the file. printf "first line\nSecond line\n" | cat -n The echo command before | outputs two lines. The cat command acts on the output to add line num...

# Length of a string $ var='12345' $ echo "${#var}" 5 Note that it's the length in number of characters which is not necessarily the same as the number of bytes (like in UTF-8 where most characters are encoded in more than one byte), nor the number of glyphs/graphemes (some of which ...

CREATE TABLE Employees ( Id int NOT NULL, PRIMARY KEY (Id), ... ); This will create the Employees table with 'Id' as its primary key. The primary key can be used to uniquely identify the rows of a table. Only one primary key is allowed per table. A key can also be composed by one...

Many databases allow to make the primary key value automatically increment when a new key is added. This ensures that every key is different. MySQL CREATE TABLE Employees ( Id int NOT NULL AUTO_INCREMENT, PRIMARY KEY (Id) ); PostgreSQL CREATE TABLE Employees ( Id SERIAL PRIMARY...

This will draw a line at the bottom of every view but the last to act as a separator between items. public class SeparatorDecoration extends RecyclerView.ItemDecoration { private final Paint mPaint; private final int mAlpha; public SeparatorDecoration(@ColorInt int color, float w...

A class is a user-defined type. A class is introduced with the class, struct or union keyword. In colloquial usage, the term "class" usually refers only to non-union classes. A class is a collection of class members, which can be: member variables (also called "fields"), mem...

There are three keywords that act as access specifiers. These limit the access to class members following the specifier, until another specifier changes the access level again: KeywordDescriptionpublicEveryone has accessprotectedOnly the class itself, derived classes and friends have accessprivate...

Classes/structs can have inheritance relations. If a class/struct B inherits from a class/struct A, this means that B has as a parent A. We say that B is a derived class/struct from A, and A is the base class/struct. struct A { public: int p1; protected: int p2; private: int p3;...

When using inheritance, you can specify the virtual keyword: struct A{}; struct B: public virtual A{}; When class B has virtual base A it means that A will reside in most derived class of inheritance tree, and thus that most derived class is also responsible for initializing that virtual base: ...